The GMC Sierra HD comes in many different configurations. The 2500 versions come in one of three body styles -- regular cab with a long bed, crew cab with a short bed and crew cab with a long bed. The 3500 body styles mirror those options but also offer the option of two extra wheels on the rear axles, useful for towing extra-heavy loads. Beyond that, both 2500 and 3500 are offered with either a 6.0L V8 making 360 horsepower or a 6.6L V8 turbodiesel making 445 horsepower and 910 pound-feet of torque. All 2500 and 3500 HD Sierras come with the option of having 4-wheel drive. Maximum tow ratings...